An imaging apparatus, such as a typical photographic camera, includes a lens barrel assembly comprising at least one barrel supporting one or more lens elements and a shutter assembly. Such a shutter assembly 5 is illustrated in FIG. 1. The shutter assembly 5 includes a ring 20 and several blades 10a, 10b, 10c that open by a variable amount to provide the desired aperture for the proper exposure. The shutter assembly is enclosed by the two housing parts 18A and 18B. The movement of the blades is controlled by a pinion gear 22 of a stepper motor 24 via use of the ring 20. The motor 24 and the pinion gear 22 are located external with respect to the shutter assembly. The ring 20 includes a sector gear with a plurality of gear teeth 20b that engages the teeth of the pinion gear 22. Thus, when the rotor 24a of the stepper motor 24 rotates, the pinion gear 22 attached to the stepper motor 24 also rotates, rotating the ring 20. The ring 20 includes posts 20a which are coupled to the slots 10a', 10b', 10c' in each of the blades 10a, 10b, 10c. The rotation of the ring 20 moves the blades, changing the size of the aperture. The blades 10a, 10b, 10c are moved in a series of steps from the closed position to achieve the desired aperture size, stay in this position for the desired exposure time and then reverse into the closed position. This configuration results in multiple parts, complex assembly and the expense due to precision alignment of the stepper motor to the shutter assembly, and the alignment of the gear teeth of the pinion gear to the poles of the stepper motor 24.
In addition, the shutter assembly is a separate part from the lens barrel assembly. Thus, the shutter assembly and the lens barrel assembly need to be precision aligned with respect to one another. This type of alignment is difficult, expensive and produces an incorrect exposure if the alignment is not performed properly. Finally, this configuration results in a large package size.
U.S. Pat. No. 4,005,448 discloses a programmable shutter and uses a stepper motor to control its position. The patent describes construction of the stepper motor for shutter actuator control and a control circuit for supplying the pulses to the stepper motor and aperture/shutter driver control circuit. More specifically, FIG. 4 of this patent illustrates that the motor comprises a stator and rotor with a central opening and, the shutter comprises three blades also forming an opening. The light passes through the central opening of the rotor and through the opening formed by the blades. This figure also shows that a ball bearing is used to maintain the proper positioning between the stator and the rotor. The proper gap between the rotor and stator is critical to allow for proper operation of the motor assembly. Thus, the stator, the ball bearing and the rotor have to be manufactured to high tolerances and carefully assembled with respect to one another. In addition, the rotation of the ball bearing has to overcome its rotational inertia, which requires power, and reduces the amount of torque generated by the motor and affects its uniformity. The assembly of many parts to form a motor in itself increases the motor size and motor complexity. Furthermore, the patent does not describe alignment between the lens barrels and the shutter assembly. As stated above, the precision alignment of the stepper motor to the shutter assembly and the precision alignment of the shutter assembly to the lens barrel assembly is expensive, and may result in an incorrect exposure if the alignment is not performed properly. Finally, the stepper motor and the shutter assembly disclosed in the U.S. Pat. No. 4,005,448 form different and separate parts from the lens barrel assembly. The shutter assembly still needs to be aligned to the lens barrel assembly. The alignment of the shutter assembly to the lens barrel has to be accomplished external to the shutter assembly. The patent does not disclose how this alignment is being done. In addition, the disclosed shutter assembly is large.
U.S. Pat. No. 4,596,449 describes a zoom drive mechanism for moving the lens units (also referred to as lens groups) to varying zoom positions and, therefore, for changing the focal length of the zoom lens system and for the fine focus adjustment. This zoom drive mechanism utilizes a stepper motor comprising a stator and a rotor. The stepper motor elements are mounted to the lens barrels. The rotation of the rotor moves the lens barrels. An improper assembly of the motor to the lens barrels can result in a wrong focal length and degraded image quality. This patent is silent with respect to the issue of aperture/shutter control.